Power supply in automotive environment

The one sentence, mostly working answer is Nat Semi Simple switcher for +5v and a 5 volt A/D with an internal 4.096v reference. Pay close attention to data sheet recommendations for reference bypassing and/or filtering.

Put a diode and a fuse in series with the battery, followed by a 20-some volt zener across the regulator input and you should be reasonably safe. I would not guarantee it for mass production though.

First verify that the supply is 12V, most motorcyles use a 6V supply. If this is the case and your current depands are small a zenner diode and a few capacitors would be my choice.

That was true at one time, but not for about the last 40 or more years.

It depends on your power requirements.

If it's a few hundred mA or less, I'd use a series diode, a reservoir capacitor and a linear regulator (78M05 etc). You could include a series L to reduce "noise".

The limits of this circuit will likely be dissipation and cooling of the regulator ((12v - 0.7v -5v)* Current)

For more than this, use a monolithic switcher (Linear Tech make some very nice ones and their website has afree simulator for designing with them). You can get wound components for these from many suppliers (e.g. Coilcraft)

You can put an LC notch filter or just a lowpass filter after the regulator, but AFTER the feedback. Do not include the filter inside the feedback loop, or it will likely oscillate. You could also put a linear regulator after the switcher, and if you use a low dropout part, the losses aren't very high. Just remember to set the output voltage of the switcher high enough to give you the headroom required for the linear reg.

On a 12V system, usually you have to be able to handle at least 24V on the input side. Put in a reverse polarity protection diode, and a fuse (or polyswitch), then follow that with a 24V power zener to ground to limit incoming voltage spikes. We used to use a MR2535L part from Motorola which was meant for this specific purpose. A datasheet can be found here:

I would think that you should be able to get standard regulators to do what you want, without having to resort to a battery supply.

Mike Anton

As someone else also stated, do not use a bridge, just a single diode in the positive supply line. You should have your circuit referenced to the vehicle ground.

There is no issue with the negative spikes, as the MR2535L is not bidirectional. It looks like a standard zener diode, so since its forward voltage is around a volt, that is what it will clamp your negative spikes to.

Sure, but only if your rectifier bridge is fast enough, and rated for the high instantaneous currents involved. But the method above is better.

Mike Anton

Look at the LM2940. It was designed for vehicular use; it has short-circuit and reverse voltage protection.